In this paper, the DCT-based real-valued discrete Gabor transform (RDGT) is briefly reviewed, and then, block time-recursive algorithms for the efficient and fast computation of the RDGT coefficients and for the fast reconstruction of the original signal from the coefficients are developed in both the critical sampling case and the oversampling case. Unified parallel lattice structures for the implementation of the algorithms are studied. Computational complexity analysis and comparison have shown that the proposed algorithms provide a more efficient and faster approach for discrete Gabor transforms as compared to the existing discrete Gabor transform algorithms.